I am new to this site and have a question about moisture barriers. Are they always necessary? I am getting ready to have an engineered walnut floor installed above grade on an osb sheeted floor. We live in Utah where it is really dry. The installer I have been talking to says that I don't need a mositure barrier. Is he right?

I would suck up the twenty bucks just to have a clean workspace if anything, heck its the easiest part of puting down a wood floor it can only help.

He may be. I have laid solid floors over subfloors that were 6 to 8 ' off the ground, earth was very dry, airflow terrific, drainage excellent. Installing a vapor barrier would have been a waste of time. If your installer will take the responsibility and warranty your floors will not cup, buckle or have any subsurface moisture issues, then forget the vapor barrier. However, it is cheap insurance and easy to do, unless your subfloor is only 18" off the ground.

The wood is going on a second floor--the floor below it is a finished walk out basement.

I guess I could just insist that he use the moisture barrier. What is the best to use, just 15# felt?

Here again, we run into terminology problems. There are two very different products and functions for moisture control under floors. One is called a moisture barrier and the other is called a vapor retarder. Any paper or felt laid over a wood subfloor which will have a woodfloor nailed over it IS NOT a moisture barrier. It is a vapor retarder. It's function is to diffuse vapor transmission from below, as well as providing a cleaner work surface and aids in reducing squeeks. A moisture barrier STOPS moisture from getting to the subfloor and wood flooring. It is usually thick sheet plastic (6 to 8 mil polyethylene), laid on the ground, on or under the concrete slab, under floating subfloors and floating floors. It is NOT to get punctured with fasteners. There are also liquid moisture barriers developed by the adhesive manufacterers that block moisture transmission. So, in conclusion, your installer SHOULD use a VAPOR RETARDER in the form of asphalt sandwiched paper placed on the subfloor. I like Aquabar for engineered.

Gary,

Thanks for that explanation. I had not read that before!

I agree with Gary.


Before your installer made that statement, where any moisture meter readings taken and written down for future reference. Did he also use a hygrometer, to check the difference in temp and humidity between the basement and the 1st floor of your home?

If not, how does he really know if it needs some kind of moisture control.